Process of recovering combined nitrogen from crude calcium cyanamide



Patented July 31, 1928.

UNITED STATES PATENT OFFICE.

GUY H. BUCHANAN, OF WESTFIELD, AND IPALIMIER W. GRIFFITH, OF ELIZABETH, NEW JERSEY, ASSIGNOBS TO AMERICAN CYANAMID COMPANY, OF NEW YORK, N. Y., A

CORPORATION OF MAINE.

PROCESS OF BECOVERING COMBINED NITBOGEN'FROM CRUDE CALCIUM CYANAKIDE. i

No Drawing.

This invention relates to a process of recovering combined nitrogen from crude calcium cyanamidecor lime nitrogen and has for .its object to render more efficient the procedures heretofore proposed.

With these and other objects in view, the invention consists in the novel steps and combinations'of steps constituting the process, all as will be more fully hereinafter disclosed and particularly pointed out in the claims.

In order that the invention may be the more clearly understood it is said 2-- The methods heretofore roposed for the production of cyanamide CN or a solution'of cyanamide from lime nitrogen have involved either extracting the lime nitrogen with water, or treatin .it with an acid solution. We have foun ,on the other hand,

that a complete extraction of the nitrogen values of limenitrogen by the use of either wateror acids is difficult to obtain. It'h'as also been our experience that except under special conditions it is not economical to treat lime nitrogen with an' acid because lime nitrogen contains large quantities of lime compounds and the'neutralization of these said compounds not only consumes lar e quantitiesof the acid, employed, but.

it orms compounds which dilute the resulting product.

In attempting to extract a substantial portion of the combined nitrogen in lime nitrogen we have further found that in order to secure a complete extraction and at the same time avoid the formation of substantial quantities of dicyandiamide and other undesirable transformation products of cyanamide, it has been necessary to work with dilute solutions of cyanamide H CN and this results in greatly increased evaporation costs. 7 a In this invention, on the other hand, We avoid these ob'ections by employing relatively strong solutions or by extracting lime nitrogen with somewhat less than the usual amount of water. That is at first we employ say 1 part of crude calcium cyanamide to 3 parts of water, and then autoclave the sludge in order to recover the unextracted nitrogen values. By thus first making 9.

Application filed February 29, 1 924. Serial'No. 896,070.

relatively strong solution of cyanamide we avoid the excessive costs of evaporating the dilute solutions heretofore employed and by autoclaving the residue, of combined nitrogen left in the sludge we avoid the loss of said nitrogen as has been the custom heres tofore, while the whole procedure avoids the making of any excessive quantities of dicyandiamide as has been the case heretofore.

As an alternative process, we may also add the crude calcium cyanamide to a water solution to which is added a reagent such as sulphuric acid, or carbon dioxide, which has the property of forming an insoluble compound with the calcium with which the cyanamide is associated and simultaneously liberating combined nitrogen. .In this alternative case, we prefer to so proportion the rates of addition of crude calcium cyanamide and the reagent that the hydrogen concentration of the solution is maintained between the limits 10 normal and 10 normal, but said hydrogen ion concentration may be above or below these limi tsdepending on the product We wish to make, all as is disclosed in a copending application Sr. No. 69l,478,'entitled Process of producing cyanamide, filed by George Barsky and Palmer W. Grifiith on the 8th day of February, 1924. v I t i In practice, we prefer to vary the proportions of water to crude calcium cyanamidev both in this alternative rocedure, and in the first mentioned proce ure according to the capacity and kind of equipment available for the extraction. In case we separate the soluble extract from the insoluble precipitates by means of a filter press or similar device, we may pump into said press the mixture of water and lime nitrogen after they have{ beenthoroughly mixed, and the temperature during the mixing is preferably prevented from rising above 40 C. .We then withdraw a substantial portion of the soluble extract, which we refer to treat further as disclosed in the a ove named co- Sending application, entitled Process of proucing cyanamide, so as to form a stable solution of cyanamide which ma be used immediately or stored as desired .The sludge from the filtering operation in both cases we autoclave to recover the nitrogen values thereof in the form of ammonia.

It will now be clear that the primary advantage of this process is that the combination of steps disclosed, permits the production of strong solutions of cyanamide H,CN

. substantially free from undesirable decombeen obtained in so far as we are aware.

position products of cyanamide, and at the same time permits the recovery of substantially all the nitrogen values otthe cyanamide. These results have never heretofojre 11 case no acid is used, the cyanamide solution should be, as above stated, about 1 part of crude calcium cyanamide to 3 parts by weight of water, but these proport ons may be one part of calcium cyanamide to one to four parts of water. In the case of the use of an acid, these proportions may vary between one part of crude calcium cyanamide to one part of acid, and one part of said cyanamide to three parts of acid.

As above stated, in order to prepare by the methods heretofore known, a solution of cyanamide H CN substantially free from undesirable decomposition products, it has been necessary to produce a solution so dilute that the subsequent utilization of the solution was uneconomical, because of high evaporation costs, The result has been essentially the same when it was attem ted to extract substantially all the soluble nitrogen values of lime nitrogen.

According to this invention, on the other hand, the solutionis never more dilute than say 5% cyanamide, when water is used and never more dilute than say 10% cyanamide when an acid is used. These solutions are found not to be prohibitive as to evaporation costs and at the same time not to produce decomposition products- In other Words, it is also well known that the maximum nitrogen that can be commercially extracted in till practice from lime nitrogen according to the prior procedures, is but from- 92% to 94% of the total values present. In this invention, on the other hand, one not only produces solutions of cyanamide, substantially tree from undesirable decomposition products thereof, but he produces strong solutions that can be evaporated within the limits of costs, and at the same time he recovers not only the soluble nitrogen values but recovers those which have never heretofore been commercially recoverable.

It is obvious that those skilled in the art may vary the details of the procedure without departing from the spirit of the invention, and therefore, it is not desired to be limited to the foregoing disclosure except as may be required by the claims,

What is claimed is 1. The process of recovering combined nitrogen which consists in providing a mixture of lime nitrogen and water containing between 100 parts and 400 parts of water by weight to each 100 parts of lime nitrogen; filtering the solution thus obtained; and subjecting the solids separated out to the action of an autoclave in the presence of additional water.

2. The process of recovering combined nitrogen from crude calcium cyanamide which consists in mixing said calcium cyanamide with water in the proportions of 100 pounds of crude calcium cyanamide to from 100 pounds to 400 pounds of water; agitating the mixture thus produced; separating out any solids present in said solution; adding water to said solids; and subjecting the mixture to the action of an autoclave to recover any combined nitrogenpresent; and recovering from said first named solution its content ofcyanamide.

3. The process of recovering combined nitrogen which consists invproviding a mix ture of lime nitrogen and water containing between 100 parts and 300 arts of water by weight to each 100 parts 0? lime nitrogen adding to said mixture an acid capable of forming an insoluble compound with the calgium present; filtering the solution of-cyanamide thus obtained; and subjecting the solids separated out to the action of an auto-' clave in the presence of additional water.

4:. The process of recovering combined nitrogen from crude calcium cyanamide, which consists in mixing said calcium cyan amide with water in the proportions of 100 pounds of crude calcium cyanamide to from 100 pounds to 300 pounds of water; adding to said mixture a reagent capable of forming an insoluble compound with the calcium pres ent; agitating the mixture thusproduced to obtain a crude solution of cyanamide; separating out any solids resent in said solution;

adding water to sai solids and subjecting the latter to the action of an autoclave to recover any combined nitrogen present.

5. The process of recovering combined nitrogen which comprises extracting lime nitrogen with water to remove a portion-of the soluble constituents thereof, and treating with water the remainder of the soluble constituents together with the insoluble constit-- uents at superatmospheric temperatures and pressures, substantially as described,

6; The process of recovering combined nitrogen rom crude calcium cyanamide which comprises extracting: lime nitrigen with water to dissolve-a portion of the cyanamide present; separating out any solids left llil in the solution from the cyanamide in said solution; treating said solids with an additional quantity of water under super-atmos pheric prmsure; and recovering the combined nitrogen thus obtained from. said solids.

l. The process of recovering combined nitrogen trom crude calcium cyimamide nevenei e which comprises extracting the calcium cyanmide under conditions and with an amount of aqueous liquid insuliicient to dissolve sub stantially all the cyanamide, separating out the solids and digesting the same with an additional amount of liquid to recover practically all of the remaining nitrogen as ammonia.

8. The recess of recovering combined nitrogen 'rom crude calcium cyanamide which comprises extracting the calcium cyanamide under conditions and with an amount of water insuflicient to dissolve substantially all the cyanamide, separating out the solids and digesting the same with an additional amount of water to recover practically all of the remaining nitrogen as ammonia.

9. The rocess of recovering combined nitrogen rom. crude calcium cyanamide which comprises extracting the calcium cyan- 2 amide with about three partsoi an aqueous liquid, separating out the solids and digesting the same with an additional amount of aqueous liquid to recover practically all of the remaining nitrogen as ammonia.

10. The process of recovering combined nitrogen from crude calcium cyanamide which comprises extracting the calcium cyanamide with about three parts of an aqueous liquid, at a temperature below 40 (3., separating out the solids and digesting the same with an additional amount of aqueous liquid to recover practically all-of the remaining nitrogen as ammonia.

In testimony whereof we ailix our sigma-35 tures.

GUY H. BUCHANAN. PALMER W. GRIFFITH. 

